Oxidation of trivalent titanium compounds contained in solid titaniferous materials



United States Patent OXIDATION OF TRIVALENT TITANIUM COM- POUNDSCONTAINED IN SOLID TITANIF- EROUS MATERIALS Olav Moklebust and HaraldBjoeraanesset, Hauge I Dalane, Norway, assignors to National LeadCompany, New York, N.Y., a corporation of New Jersey dation of trivalenttitanium compounds contained in concentrates produced by thermoreduction of titniferous ores such as ilmenite. The instant process isparticularly useful in the production of a titaniferous compositionwhich is amenable to digestion by concentrated mineral acids.

' Titaniferous slags, sintered masses, or other types of 'agglorneratesor finely divided materials produced by thermo reduction of titaniferousores or ore concentrates with a carbonaceous reducing agent such ascoke, with or -without simultaneous supply of heat by burning liquid orgaseous fuels. Such reduction operations may take place 'in a smeltingfurnace and in such cases the titanium dioxide rich slag and themetallic iron are normally tapped separately. In another procedure thereduction may be carried out without any smeltering or sintering, forinstance, in a rotating furnace. In this case the reduced "concentrateis normally crushed, subsequently washed and separated magnetically orby other mechanical means in order to recover a titanium dioxide richconcentrate and a concentrate of metallic iron.

Such concentrates rich in titanium dioxide can also be produced bymixing a crushed titaniferous ore concentrate and small amounts offluxes, such as sodium chloride and/or sodium carbonate, agglomeratingthe mixture so formed and heating the same in the presence of reducingagents so as to achieve formation of finely divided metallic iron whichis subsequently separated from the titanium oxide concentrate bymechanical means.

In order to obtain high grade titanium oxide concentrates by any of theprocesses just mentioned, it is important that a substantial part of theiron content be reduced to the metallic state. Under strongly reducingconditions, a considerable part of the titanium oxides in theconcentrate are also reduced to oxidic compounds of trivalent titanium.It has been observed that between 50 and 80 percent of the total amountof titanium present in the titanium oxide concentrate resulting from thereduction, may be present in the trivalent state. When hydrolyzingtitanium sulfate solutions, trivalent titanium is not precipitated andwill consequently be lost with the socalled mother liquor. The amountsof trivalent titanium which are lost may be considerable and thepresence of same is in large quantities obviously not desirable in theti o n of titaniferous concentrates, it has been proposed to PatentedApr. 18, 1961 blow air through the titanium solution in order to oxidizethe trivalent titanium compounds. Another proposal has been to addvarious chemical oxidizing'agents; however, the use of same is oftenexpensive and may very well impair the quality of the final products.Therefore. until the development of the instant invention, it has beenimportant to use titanium oxide rich concentrates containtaining onlymoderate amounts of trivalent titanium compounds. Still another proposalwas to oxidize the material containing trivalent titanium compounds andair at temperatures of 150 C. or higher. However, it was noted thatmaterials oxidized at such elevated temperatures are not easilydigestible-in sulfuric acid.

Accordingly, an object of the instant invention is to provide a processfor rendering materials containing solid trivalent titanium containingvalues to a form amenable to digestion in concentrated mineral acids.Another object is to provide a simple method for converting thetrivalent titanium compounds contained in materials of the typedescribed to tetravalent compounds. These and other objects of theinstant invention will become apparent in the following more completedescription and from the examples.

Broadly, the instant invention relates to a method for renderingmaterials containing solid trivalent titanium compounds amenable todigestion with concentrated mineral acids which comprises admixing suchmaterials in a finely divided state with sufficient water to form a wetmass, contacting the wet mass with oxidizing gas to oxidize trivalentcompounds to tetravalent compounds while maintaining the temperatureduring the oxidationbelow 100 C. In a more specific embodiment of theinstant invention, the oxidation is efiected in the presence of oxi-'dation catalysts.

According to the instant invention, trivalent titanium compoundscontained in solid titaniferous materials may be subjected to oxidationunder controlled temperatures in the presence of electrolytes such asdilute solutions of mineral acids or dilute solutions of mineral saltswith the result that there is obtained a high recovery of acid solubletitanium compounds.

According to the instant process, the oxidation of the trivalenttitanium compounds takes place in the presence of controlled amounts ofwater or steam and an oxygen containing gas such as air whilemaintaining the oxidation temperature below about 100 C. Addition ofwater or steam should be made in such a way to maintain the mass to beoxidized in a thoroughly wet condition; however,

introduction of water in such amounts that a pasty con- 50 :sistencywill result is to be avoided since this situation oxygen containinggases.

would counteract the reaction of the material with the If the theoxidation is carried out under too dry a condition, for instance byrapid evaporation of the water, the process may be retarded or evenstopped. It is however possible to admix the amount of water required inthe oxidation reaction with the material in advance. In this case, thematerial which is being oxi .dized is normally maintained in the form ofa static layer of some suitable thickness. In representative cases, amoisture content of 20-30 percent of the dry weight of the concentratehas been found suitable.

The rate of oxidation is accelerated when the material is stirred orploughed since this action facilitates access of air and exposes freshunoxidized material. The manner of-stirring and aerating the material isof importance when choosing the most effective thickness of the layer ofmaterial. Experiments have indicated that a suitable thickness of astatic bed when no stirring or agitation is employed is between 10 and25 millimeters.

Theoxidation rate also increases with increased temperatures below 100C. It has been observed that effective oxidation takes place between 40and C. and

particularly in the range 60-85 (3. During the oxidation process, heatis developed and generally no additional heat is applied from anexternalsource. It is however of importance that the thickness of thelayer of material under treatment he so 'controlled'that excessive heatlosses do not occur with the result that the temperature would drop to apoint which is not suflicient to maintain the oxidation reaction.Further, it is important that sufl'icient quantities of oxidizing gassuch as air be available to provide intimate contact with the materialto be oxidized.

It has been found quite unexpectedly that the oxidation of trivalenttitanium materials of the type disclosed herein may be considerablyaccelerated by an addition of small amounts of electrolytes such as forexample dilute solutions of mineral acids and mineral salts. Among theelectrolyte solutions which have been found particularly effective arethose containing sulfuric acid, hydrochloric acid, sulfates, chlorites,chlorates, and the like. Dilute sulfuric or hydrochloric acid inquantities of 0.1-2 percent H 50 or HCl (calculated on the weight of theconcentrate) seem preferable, but even traces of electrolyte in thewater appeared to have a beneficial influence on the rate of theoxidation process.

The water addition to the mass may be done in one step as has beendescribed or may also be extended over the whole period of oxidation,that is from the start to the interruption of the oxidation reaction. Insuch practice, it becomes important to closely control the moisturecontent of the material, that is to take steps to see that the materialneither becomes too wet or too dry but rather that it maintains amoisture content dependent upon the specific material being handled andthe temperature which it is proposed to maintain during oxidation. Thematerial may be moistened by spraying a liquid over the surface in theform of small droplets using a spray nozzle and at the same timepelletizing the moist material. Pellets which are moistened throughoutwithout having a pasty consistency may be prepared in this manner. Thesepellets should have a size between 1 and 10 millimeters and shouldpreferably be in the 2-5 millimeter range. Such moist pellets of theparticle size indicated have proved suitable for quick oxidation and areconveniently placed in layers of suitable thickness.

The particlesize of the concentrate has been found to be significant inactual operation of the oxidation process. Initially finely dividedmaterial is preferred although thismay be pelletized as just indicated.The concentrate should have a particle size not in excess of about 50microns and should preferably be in the range of 2 to 10 microns.

X-ray diffraction patternsindicate that when the oxidation is carriedout according to the present invention there is no latice rearrangement.Material both before and 'after the oxidation is identified as (Fe, Mg)-2TiO admixed with substantial quantities of titanium oxides. Anatase,rutile, and free Tigog could not be traced. It is known that compoundsof the type indicated by the formula (Fe,.Mg)-2TiQ are easily digestedby sulfuric acid treatment as is known to the art.

Still another unexpected advantage of the method of the presentinvention is the observation that material in the oxidized trivalentstate as produced may be subsequently heated at temperatures up to about250 C. without any apparent formation of free T10 or other physical orchemical changes in the material, which would result in subsequent lowrecoveries when the material is subjected to sulfuric acid digestion.

In order to illustrate the advantagesof the instant invention thefollowing examples are offered.

Example I -in tne trivalent state (calculated as T i was thoroughlywetted with dilute sulfuric acid (1:20) and the material was then spreadout in a layer of 12 millimeters thickness. Upon contact with air theoxidation of the trivalent compounds began and the oxidation wasaccompanied by an increase in temperature, the temperature of thematerial reaching a peak of .84" C. in about fifteen minutes. At thistime it was determined that after the oxidation the amount of trivalenttitanium had fallen from 55.0 percent to 24.7 percent of the totalamount of titanium. This corresponded to about 18.5 percent trivalenttitanium calculated as TiO in the final product.

The oxidized concentrate was digested'with sulfuric acid according toknown laboratory methods using a thermos flask as the digestion chamber.Upon analysis it was determined that about 96.8 percent of the TiO, wasacid soluble. This high content of soluble TiO was proof of the easilydigestible. compounds which are. in the oxidized material.

Exampl I A sample of TiO;; rich concentrate analyzing in total 80.5percent TiO of which 78.0 percent was present--in the trivalent state(calculated as TiO Was rolled in a pelletizing apparatus to form pelletsof the 2-3 millimeter size range. 7 During the pelletizing operation,dilute hydrochloric acid (1:20) was added. The temperature duringoxidation rose to about 68 C. The pellets were then placed in a layer ofabout20 millimeters thickness and oxidation commenced. The temperaturereached about 68 C. in short order and continued upward to about 84 C.in nineteen minutes. After oxidation of the pellets it was determinedthat the amount of trivalent titanium had decreased from 78.0 percent to25.5 percent of the total amount of titanium. This corresponded to about19.5 percent trivalent titanium calculated as TiO- Digestion tests ofthis material were conducted as indicated in Example I and it wasdetermined that about 96.0 percent of the titanium values in theoxidized prod-- not were acid soluble TiO Example '11] A sample of theoxidized concentrate described in Example II was furtherheated to 200 C.and kept at this temperature for half an hour. The heated material wasthen found to contain 25.2 percent of total titanium in the form oftrivalent titanium (calculated as TiO Sulfuric acid digestion ofthismaterial indicated that about 95.6 percent of the titanium waspresent as acid soluble TiO For purposes of comparison, the sample ofthe same Ti0 rich concentrate as was employed in Example I was initiallyheated in air to about C. The temperature of the material increasedfurther in a. rapid manner to about 500 C. and this temperature wasmaintained for an additional thirty minutes. Upon cooling the materialwas found to have completely oxidized. The oxidized concentrate wasdigested with sulfuric acid according to the same technique as describedin Example I. The content of soluble Ti0 was determined to be as low as52 percent of the total amount of titanium oxides calculated as Ti0 inthe concentrate. This result indicated considerable formation ofsparingly soluble TiO during the oxidation period.

It has thus been shown that the instant process provides a simple andeffective process for converting trivalent titanium values totetravalent values whereby the subsequent digestion or solubilization ofthe titanium modifications and variations may be employed within thescope of the following claims.

We claim:

1. Method for rendering a material consisting essentially of a finelydivided titanium concentrate having a particle size not in excess ofabout 50 microns and containing solid trivalent titanium oxide amenableto digestion with concentrated sulphuric acid which comprises wettingthe finely divided concentrate with water and a small amount ofoxidation accelerator without dissolving the concentrate and withoutforming a slurry, contacting the so wetted concentrate, prior todigestion, with oxygen containing gas to oxidize the trivalent compoundsto tetravalent while maintaining the temperature during oxidation below100 C.

2. Method according to claim 1 wherein the temperature is maintainedbetween about 40 C. and about 90 C. Y

3. Method according to claim 1 wherein the particle size is between 2and 10 microns.

4. Method according to claim 1 wherein the oxida- 6 tion accelerator issulphuric acid, said acid being present not in excess of 2 percentcalculated on the weight of the material under treatment.

5. Method according to claim 1 wherein the oxidation accelerator ishydrochloric acid, said acid being present not in excess of 2 percentcalculated on the weight of the material under treatment.

6. Process according to claim 1 wherein the amount of oxidationaccelerator is between 0.1 percent and 2.0 percent calculated on theweight of the material ,under treatment. 2

References Cited in the file of this patent UNITED STATES PATENTS1,656,572 Schultze Jan. 17, 1928 2,125,340 Hager Aug. 2, 1938 2,149,370Smith Mar. 7, 1939 2,339,808 Ravnestad et al. Jan. 25, 1944 2,589,910Schnieder Mar. 18, 1952 2,724,636 Mullin et al. Nov. 22, 1955

1. METHOD FOR RENDERING A MATERIAL CONSISTING ESSENTIALLY OF A FINELYDIVIDED TITANIUM CONCENTRATE HAVING A PARTICLE SIZE NOT IN EXCESS OFABOUT 50 MICRONS AND CONTAINING SOLID TRIVALENT TITANIUM OXIDE AMENABLETO DIGESTION WITH CONCENTRATED SULPHURIC ACID WHICH COMPRISES WETTINGTHE FINELY DIVIDED CONCENTRATE WITH WATER AND A SMALL AMOUNT OFOXIDATION ACCELERATOR WITHOUT DISSOLVING THE CONCENTRATE AND WITHOUTFORMING A SLURRY, CONTACTING THE SO WETTED CONCENTRATE, PRIOR TODIGESTION, WITH OXYGEN CONTAINING GAS TO OXIDIZE THE TRIVALENT COMPOUNDSTO TETRAVALENT WHILE MAINTAINING THE TEMPERATURE DURING OXIDATION BELOW100*C.